As is well known, in metal etching industry they often have resort to chemical etching processes.
For instance, this is the case with electronic industry in the production of printed circuit boards. In an etching machine or line an active etching solution comprising ammonium chloride and small percentages of other chemical agents is introduced into suitable continuous baths, in which solution duroplast/copper assemblies are dipped, whose portion made up of the thin copper sheet provided on them is removed from the same through selective etching resulting from chemical attack carried out by the solution, so as to obtain the formation of conductive paths according to a previously established topography, i.e. electric circuits.
The active etching solution, after removing a portion of copper from the duroplast, that is the support, leaves the last bath of the etching machine or line as a "spent" solution, i.e. as a copper-containing solution, its concentration being up to 150 g of copper/liter, as cupric chloride, that is as a very poisonous solution.
It is fully evident that it is necessary to recover both chemical agents and the metal or metals contained in such spent solutions. Total recovery is not only an economic factor, but it is mainly an ecological necessity. Such recovery satisfies the requisites of avoiding dispersion of such poisonous solutions into the environment, and of safeguarding metal resources as well, which surely are not endless.
Up to the present time the subject solutions, when not dispersed into the environment, have been treated according to the so-called "knock-down process". The spent solution is mixed with soda in the amount which is considered necessary. Ammonia evolves from the solution (which ammonia can be recovered). Copper or any other metal is "recovered" as the hydroxide, that is in an extremely degraded state, and a liquid made up of sodium chloride contaminated with ammonia and copper is left behind, said liquid being conveyed into a sewer or into a river. Such procedure also turns out to be detrimental to the environment.
Another process already known is the subject of a patent of the same Applicant as that of the present application. However, such process is very complicated and costly to realize, as well as very complex as regards the treatment, and unsuitable to "miniaturization".